1. Field
Embodiments of the present invention generally relates to the field of imagery. More specifically, embodiments of the present invention refer to blocking undesirable wavelengths of light from reaching an image sensor and minimizing retroreflection in an image device.
2. Background
Dichroic cut filters are used in optical systems of image devices to selectively pass light of a specified range of wavelengths while reflecting other wavelengths. In image applications, a commonly-used dichroic cut filter is an ultraviolet/infrared (UV/IR) cut filter. UV/IR cut filters are used to block UV and IR wavelengths of light and to transmit visible light. Conventional UV/IR cut filters are thin films with varying refractive indices stacked on a transparent surface to achieve a particular wavelength frequency response.
The passband of a UV/IR cut filter may change depending on the angle of incidence of light impinging thereon. As the passband characteristics of the filter's transmission curve change with varying angles of incidence, the UV/IR cut filter may leak and transmit unwanted light to a detector when light is received outside of the optimal range of angles. The color fidelity of an image then becomes a greater issue. What is needed is a UV/IR cut filter that reduces transmission of unwanted wavelengths of light.